Image decoding method, image coding method, image decoding apparatus, image coding apparatus, and image coding and decoding apparatus

Abstract

The image decoding method includes determining a context for use in a current block to be processed, from among a plurality of contexts, wherein in the determining: the context is determined under a condition that control parameters of a left block and an upper block are used, when the signal type is a first type; and the context is determined under a third condition that the control parameter of the upper block is not used and a hierarchical depth of a data unit to which the control parameter of the current block belongs is used, when the signal type is a third type, and the third type is one or more of (i) “merge_flag”, (ii) “ref_idx_l0” or “ref_idx_l1”, (iii) “inter_pred_flag”, (iv) “mvd_l0” or “mvd_l1”, (v) “intra_chroma_pred_mode”, (vi) “cbf_luma”, and (vii) “cbf_cb” or “cbf_cr”.

The invention claimed is: 
     
       1. A decoding method for decoding a control parameter for controlling decoding of an image, the decoding method comprising:
 determining a context for a current block in the image, from among a plurality of contexts; and 
 performing arithmetic decoding on a bitstream corresponding to the current block, using the determined context to obtain the control parameter for the current block, 
 wherein the determining further includes:
 determining a signal type under which the control parameter of the current block is classified; 
 determining the context by using both of decoded control parameters for a left block and an upper block, when the signal type is a first type, the left block being a neighboring block to the left of the current block, and the upper block being a neighboring block on top of the current block; 
 determining the context by using a predetermined fixed value, without using any of the decoded control parameters for the left block and the upper block, when the signal type is a second type different from the first type; and 
 determining the context by using a hierarchical depth of a data unit to which the control parameter for the current block belongs, without using both of the decoded control parameters for the left block and the upper block, when the signal type is a third type different from the first type and the second type regardless of a decoding mode used to decode the current block, 
 
 wherein one of a split flag and a skip flag is classified under the first type, the split flag indicating whether or not the current block is partitioned into a plurality of blocks, and the skip flag indicating whether or not the current block is to be skipped, 
 wherein a residual flag is classified under the second type, the residual flag indicating whether or not luma coefficient data and chroma coefficient data are included in the current block, 
 wherein a luma coefficient flag and a chrominance coefficient flag are classified under the third type, the luma coefficient flag indicating whether or not the current block includes a non-zero luma coefficient, and the chrominance coefficient flag indicating whether or not the current block includes a non-zero chrominance coefficient, and 
 wherein a first number of contexts for the luma coefficient flag is different from a second number of contexts for the chrominance coefficient flag. 
 
     
     
       2. A decoding apparatus for decoding a control parameter for controlling decoding of an image, the decoding apparatus comprising:
 a context determination unit configured to determine a context for a current block in the image, from among a plurality of contexts; and 
 an arithmetic decoding unit configured to perform arithmetic decoding on a bitstream corresponding to the current block, using the determined context to obtain the control parameter for the current block, 
 wherein the context determination unit is configured to:
 determine a signal type under which the control parameter for the current block is classified; 
 determine the context by using both of decoded control parameters for a left block and an upper block, when the signal type is a first type, the left block being a neighboring block to the left of the current block, and the upper block being a neighboring block on top of the current block; 
 determine the context by using a predetermined fixed value, without using any of the decoded control parameters for the left block and the upper block, when the signal type is a second type different from the first type; and 
 determine the context by using a hierarchical depth of a data unit to which the control parameter for the current block belongs, without using both of the decoded control parameters for the left block and the upper block, when the signal type is a third type different from the first type and the second type regardless of a decoding mode used to decode the current block, 
 
 wherein one of a split flag and a skip flag is classified under the first type, the split flag indicating whether or not the current block is partitioned into a plurality of blocks, and the skip flag indicating whether or not the current block is to be skipped, 
 wherein a residual flag is classified under the second type, the residual flag indicating whether or not luma coefficient data and chroma coefficient data are included in the current block, 
 wherein a luma coefficient flag and a chrominance coefficient flag are classified under the third type, the luma coefficient flag indicating whether or not the current block includes a non-zero luma coefficient, and the chrominance coefficient flag indicating whether or not the current block includes a non-zero chrominance coefficient, and 
 wherein a first number of contexts for the luma coefficient flag is different from a second number of contexts for the chrominance coefficient flag. 
 
     
     
       3. A decoding apparatus for decoding a control parameter for controlling decoding of an image, the decoding apparatus comprising:
 processing circuitry; and 
 storage coupled to the processing circuitry, 
 wherein the processing circuitry performs the following using the storage:
 determining a context for a current block in the image, from among a plurality of contexts; and 
 performing arithmetic decoding on a bitstream corresponding to the current block, using the determined context to obtain the control parameter for the current block, and wherein the determining further includes: 
 determining a signal type under which the control parameter for the current block is classified; 
 determining the context by using both of decoded control parameters for a left block and an upper block, when the signal type is a first type, the left block being a neighboring block to the left of the current block, and the upper block being a neighboring block on top of the current block; 
 determining the context by using a predetermined fixed value, without using any of the decoded control parameters for the left block and the upper block, when the signal type is a second type different from the first type; and 
 determining the context by using a hierarchical depth of a data unit to which the control parameter for the current block belongs, without using both of the decoded control parameters for the left block and the upper block, when the signal type is a third type different from the first type and the second type regardless of a decoding mode used to decode the current block, 
 
 wherein one of a split flag and a skip flag is classified under the first type, the split flag indicating whether or not the current block is partitioned into a plurality of blocks, and the skip flag indicating whether or not the current block is to be skipped, 
 wherein a residual flag is classified under the second type, the residual flag indicating whether or not luma coefficient data and chroma coefficient data are included in the current block, 
 wherein a luma coefficient flag and a chrominance coefficient flag are classified under the third type, the luma coefficient flag indicating whether or not the current block includes a non-zero luma coefficient, and the chrominance coefficient flag indicating whether or not the current block includes a non-zero chrominance coefficient, and 
 wherein a first number of contexts for the luma coefficient flag is different from a second number of contexts for the chrominance coefficient flag.